The present disclosure relates generally to communication systems, and more particularly, to a downlink frame structure and method of downlink transmission for managing communications with user equipment in a wireless communication system.
Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.
In wireless communication systems employing legacy LTE, a plurality of UEs served by a particular eNodeB may receive data from the eNodeB over a downlink channel called the Physical Downlink Shared Channel (PDSCH). In addition, control information associated with the PDSCH may be transmitted to the UEs by the eNodeB via a Physical Downlink Control Channel (PDCCH). The control information included in the PDCCH may include one or more uplink or downlink resource element (RE) grants for an LTE subframe. In legacy LTE, each LTE subframe includes a control region during which the control information is transmitted via the PDSCH and a data region during which data is transmitted to one or more of the UEs.
In legacy LTE systems, however, each UE may be required to search a large number of regions within the control region to determine whether control information pertinent to the UE is present. Specifically, for instance, the UE may be informed of a number of regions within the control region of a subframe and may not be provided with the location of its corresponding PDCCH. Instead, the UE may locate its PDCCH by monitoring a set of PDCCH candidates in every subframe. Such decoding may be referred to as blind decoding.
However, blind decoding of PDCCHs may be inefficient as radio network temporary identifiers may be unknown to the UE. Additionally, decoding a large portion (e.g., nearly all control channel elements (CCEs)) to locate a UE specific PDCCH may result in degradations in wireless communication quality. For instance, for UE applications requiring particularly low latency communication, with a large number of possible PDCCH locations, blind searching may be a significant system burden, leading to excessive power consumption at the UE and lower maximum data communication rates in the system. For example, in legacy LTE systems, each UE may be required to perform up to 44 (or more) blind decodes for each subframe. Attempts to reduce latency based on this legacy structure may be difficult, however, because as a transmission time interval (TTI) associated with each symbol of a subframe decreases, the individual UEs may simply not have the processing resources to perform the operations associated with these 44 or more blind decodes within a time interval required for receiving and decoding data on the PDSCH.
As such, improvements in the downlink frame structure and downlink transmission methods are desired.